Unmanned and autonomous cargo ships may transform the maritime industry,
but there are issues regarding reliability of machinery which must frst be solved.
This paper examines the efect of voyage length on the reliability of machinery
with redundancy on unmanned ships. The limiting efects of dependent failures on
the improvement of reliability through the use of redundancy is also explored. A
strong relationship between voyage length and probability of independent failures
in systems with redundancy is shown. Increased redundancy can easily counteract
this negative efect of long unmanned voyages on reliability. Dependent failures,
however, are not afected by increased redundancy. The contribution of dependent
failures on the total probability of failure is found to easily exceed the contribution
from independent failures if even a slight proportion of the failures is dependent.
This has serious implications for unmanned ships where the possibility of corrective
maintenance is very limited and the consequences of mechanical failures on, e.g. the
propulsion of the ships can therefore be expected to be more severe than on conventionally manned ships. Redundancy in itself may not be enough to provide the reliability of machinery systems required for unmanned operation and other solutions
must therefore be found.
Autonomous unmanned underwater vehicles (UUVs) play a vital role in diverse underwater operations; localization is of great interest for UUVs mirroring the trend seen in self-driving surface and aerial vehicles. Unlike their land and aerial counterparts, underwater environments lack reliable Global Navigation Satellite Systems (GNSS) due to radio wave attenuation in water. Hence, alternative localization methods are imperative for both navigation and operational purposes. This study thoroughly reviews sensor technologies for underwater localization, including sonar, Doppler velocity log, cameras, and more. Different operations necessitate distinct localization accuracies and vehicle and sensor choices. Environmental factors, such as turbidity, waves, and sound disturbances, impact sensor performance. Conclusions are given on the coincidence between operational requirements and sensor specifications, with special attention to the open concerns. These considerations include aspects such as the line of sight for acoustic positioning systems and the requirement for a feature-rich environment for visual sensors. Lastly, a prediction for the future of underwater localization is given, where the tendencies indicate lower costs for sensors, making operation-specific vehicles more attractive, which aligns with an increased demand for cost-efficient autonomous offshore operations.